I heard the other day that the 4M number they floated was a totally unrealistic low-ball. It could well be many 10s of millions of current & former government employees. A reporter stated that a FORMER congressional staffer who has been out of government employ for nearly a decade received notice from the government notifying him that his records were stolen.
Mark
Part of that depends on how far back the records pull goes - if it is 20 years, then yes, easily 4 million current federal employees, several times that for military and defense contractors.